1. Technical Field
The present invention relates to cooling apparatus.
2. Prior Art
Various proposed cooling apparatus have taken advantage of the Joule-Thomson effect. In such coolers a gas is adiabatically throttled through an orifice from a high pressure to a low pressure. If the initial temperature of the gas is below its inversion temperature, then a fall in temperature takes place as the gas is passed through the orifice. Such a cooler requires a supply of high pressure gas since the fall in temperature of the gas in passing through the orifice is proportional to the drop in pressure.
Because of the need for a gas supply such cooling apparatus is mainly used in static applications.
In order for a Joule-Thomson effect cooler to work efficiently it is necessary for the gas which is throttled to be particularly pure because the orifice through which it is throttled has to be small and is therefore easily blocked by foreign bodies or impurity gases and vapours which freeze in the orifice. For instance if nitrogen is used no carbon dioxide can be present as this may freeze. Likewise water is also to be avoided not only because its freezing can block the throttle but also because its expansion on freezing can damage the cooler.
To make such a cooler portable, a high pressure cylinder of gas could be used. However this is a relatively heavy and bulky way of transporting the gas.